Inlet screen for intensifying x-ray images

ABSTRACT

An inlet screen for intensifying X-ray images has a layer applied upon a carrier and caused to light by X-rays, as well as a photocathode combined with the Layer. The invention is particularly characterized by the provision of a layer between the luminous layer and the carrier and absorbing the light of the luminous layer.

United States Patent Christgau et a].

INLET SCREEN FOR INTENSIFYING X-RAY IMAGES Inventors: Hermann Christgau, Furth;

Wolfgang Schubert, Frauenaurach; Aribert Stachowiak, Erlangen, all of Germany Assignee: Siemens Aktiengesellschaft, Munich,

Germany Filed: Feb. 8, 1974 Appl. No.1 440,707

Foreign Application Priority Data Feb. 13, 1973 Germany 2307026 US. Cl. 250/483 Int. Cl. H01j 1/62 Field of Search 250/483, 487, 458, 460

[56] References Cited UNITED STATES PATENTS 3,783,297 1/1974 Houston 250/483 Primary E.\'aminerArchie R. Borchelt Attorney, Agent, or Firm-V. Alexander Scher 5 7 ABSTRACT An inlet screen for intensifying X-ray images has a layer applied upon a carrier and caused to light by X- rays, as well as a photocathode combined with the Layer. The invention is particularly characterized by the provision of a layer between the luminous layer and the carrier and absorbing the light of the luminous layer.

5 Claims, 3 Drawing Figures KIT INLET SCREEN FOR INTENSIFYING X-RAY IMAGES This invention relates to an inlet screen for intensifying X-ray images having a layer applied upon a carrier and excited to luminescence by X-rays and a photocathode combined therewith. Electrons are released in such layers the quantity of which depends upon the intensity of illumination and thus upon the distribution of brightness in a picture. These electrons are usually represented in an image amplifier electronic-optically upon a second luminous layer sensitive to electrons, which is then inspected or photographed. It can also be an inlet screen for television photography or an intermediate screen for the connection of a brightness amplifier. Instead of the second luminous screen when further amplifying steps are used. it is possible to provide screens in various arrangements which are excitable for sending secondary electrons.

The image quality of one of the above amplifying de vices which is expressed in the modulation transmission function, results from the image transmission properties of the individual stages. In the usual image amplitier the picture is produced in stages, namely, X-rays are changed into electrons, the electrons are represented in an outlet screen and in the outlet screen the electrons are changed into a visible picture, so that there is a total of three stages. So far attempts have been made in each stage to do everything possible to provide the best possible pictures. Thus, for example, the inlet screen has been given the shape of a calotte with a non-uniform radius. This greatly improves the electronic optic being imaged. Furthermore the surface of this calotte coated with a luminous layer has been roughened to keep back reflections. Measures have also been carried out in the construction of other parts of the image amplifier to improve the imaging.

An object of the present invention is to provide further means for improving image transmitting properties.

The present invention is based substantially on the consideration that the surface of the carrier upon which the luminescent layer is applied is struck by about one half of theluminescent light, while the other half is substantially absorbed at the edge surface of the luminous layer toward the photocathode layer. When the carrier surface is smooth, the striking light rays are reflected. This means that light rays striking under greater angles mostly between the carrier surface and the edge layer are reflected between the luminous layer and the photocathode. This helps toward a general pic ture brightness, but not to an improvement of transmitted information. On the contrary, this is diminished since the brightness makes the background brighter and is not combined any more with a direct representation of the details of the picture.

In accordance with the present invention an improvement is achieved by providing the inlet screen of the image amplifier between the luminous layer and the carrier with a layer absorbing the light of the luminous layer. This provides that the luminescent light, striking close to the carrier, is not reflected any more at least to a large extent and thus can not increase the brightness of the background. This improves the picture.

In carrying out the present invention it was considered that the part of the light striking the carrier surface consists of the sum of the spectral intensity of the luminescence of the luminous substance and the spectrally dependent absorption at the intermediate layer. In case of a luminous substance consisting of cesium iodide when activated with sodium, can be used, for example, berillium, titanium, nickel, carbon or zirconium, since they have corresponding absorption. With the exception of carbon these substances react, however, with an X-ray luminous pigment, such as cesium iodide. For technological reasons, namely, due to easier and reproduceable coating procedure, gold was found to be a useable substance for intermediate layer. Also can be used elements or compounds which have an absorption of neutral-gray character in the visible part of the spectrum. s

The emission maximum of the luminous substance then is safely in the absorption range of the intermediate layer. The extent of absorption can be adjusted by the thickness of the coating of the material for the intermediate layers. As examples of useable substqnces can be mentioned chromium,'carbon, titanium monox ide.

As is apparent from the. above, the selection of material from which the intermediate layeris made depends from the used carrier material and the material of the luminous substance. As luminous substances can be used those the spectral emission of which, when engaged by X-rays, is adapted to the spectral sensitivity of the actual photocathode layer. In addition to the above-mentioned cesium iodide can be used, among others, zinc sulfide and Zinc cadmium sulfide which are activated with silver. Occasionally when using the lastmentioned luminous substances intermediate layers were used which were applied'between the luminous layer and the photocathode layer and consisted. for example, of aluminum oxide, magnesium oxide of silicic acid, so as to separate the two substances and prevent them from reacting with each other. As carrier all substances can be used which have sufficient mechanical firmness to be stable in vacuum, such as glass, titanium,

beryllium or aluminum. It is only necessary that in addition to the above properties they should have the best possible transmission for Xrays. In accordance with the present invention the carrier which is occasionally called substratum can be roughened upon the side which is to be coated with the luminous substance whereby the roughness can have the depth of about 3 to 40 m. This roughness can be carried out by all known methods, for example, by the application of particles transmitted by a gas or liquid ray, by rough stamping or by corroding with the use of hydrochloric acid and hydrofluoric acid, or also by solutions of alkali-ammonium, iron, and chromium salts, or plasma spraying of colored metal oxides for producing a rough surface which at the same time has the desired absorption due to its coloring. As the photocathode layer can be used a known combination of antimony and alcali metals, such as cesium, sodium, potassium.

The invention will appear more clearly from the following detailed descriptions when taken in connection with the accompanying drawing showing by way of example only, preferred embodiments of the inventive idea.

In the drawing:

FIG. 1 is a diagrammatic section through an image amplifier having an inlet screen which is constructed in accordance with the present invention.

FIG. 2 is an enlarged section through the inlet screen.

FIG. 3 is a diagrammatic section through a steaming. device for applying the intermediate layer and possibly also the luminouslayer.

FIG. 1 shows the vacuum-tight casing l of the image amplifier. Theinlet screen 2 consisting of a combination of layers, is located behind the inlet window 3. Behind the window 3 and the screen 2 are located ring electrodes .4, S and the anode 6 which is also ringshaped. The end of the device is constituted by a luminous layer 7 which at theside directed. toward the inlet screen is coated by a thin aluminum layer 8. The opposite side of the screen 7 is limited by the end window 9 of the image amplifier. The-inlet screen 2 is held at the inner wall of the casing l by bars extending from the wall to the carrier 12. Two bars 10 and Here shown in. FIG, 1. The carrier. 12 is covered by a layer 13 of gold which is followed by a luminous layer 14 covered by a photocathode layer 15. The carrier 12 of the inlet screen 2 consists of a calotte of aluminum sheet curved according to requirements of electronic optics. Prior to the coating with the luminous layer it is cleaned and its fat removed in a cleaning solution in a .known manner. Afterthe pickling it is thoroughly rinsed with water and the inwardly curved side of the carrier 12 is coated with a caustic solution and further treated in a known manner until the roughening depth of 3' ,to 40 ,u.m, in this caseZOum, hasbeen reached. To complete the roughening it is rinsed with water and then the carrier 12 is dried. I w

The application of intermediate layer l3 consisting of gold and takes place under the bell jar 16 in high vacuum, produced by the pump 17. For that purpose the carrier 12 is placed upon supports, two of which, designated as l8 and 19, are shown in FIG, 3. The actual steaming with gold takes place by a steamer 21 driven by the current source and having a steaming shuttle 22 containing the substance 23 to be steamed, namely, gold. It is steamed upon the carrier 12, as shown by broken lines 24. In the illustrated example with the carrier 12 having a 200 mm diameter, a sufficiently absorbing layer is produced by steaming 500 mg gold. The distance of the carrier l2 from the substance 23 which is being steamed on, amounts to 230 mm and is maintained by supports 18 and 19 (FIG. 3).

After. the intermediate layer 13 the luminous layer 14 is steamed on. During the manufacture of the image amplifier the screen is built into the container 1 prior to theapplication of the photocathode layer 15 which consists, as is known, of antimony and cesium.

The amount of gold applied as the intermediate layer is so measured that a sufficiently thick coating of the rough substrata surface is produced. In the present case this is an amount which is condensed when in a presteaming'sub-strata distance of at least about mm about 400 mg are evaporated. In the technology used gasing must take place prior to the introduction into the molten vacuum casing l of the image amplifier. As shown in FIG. 2 a sufficient covering is already provided when the surface of the carrier .12 to be covered by a luminous layer 14 is provided by roughening with a plurality of closely located bag-like, openings 25 the bases of which are covered with the absorbing layer 13. This division of the layer 14 upon the bases 26 of the openings 25 has an advantage produced by intermediate walls 27; which cause the guiding of the luminescent light. up to the height of these intermediate walls 27 only within the hollow space, whereby this light can be thrown back and is spread also in theluminous layer 14 over the intermediate walls only as a cone of a small angle. The advantage consists in that the light emitted by x-ray excitation has a preferred orientation to the photocathode 15.

What is claimed is:

1. An inlet screen for intensifying X-ray images, comprising a carrier, a layer carried by said carrier and adapted to luminesce under the action of X-rays, a photocathode connected with said layer, and another layer located between said carrier and the first-mentioned layer and absorbing the light of the first-mentioned layer, said carrier being roughened prior to the application of the second-mentioned layer, the depth of the roughening ranging between 3 and 40pm, said rough-' ening forming holes with bases, said bases being covered with the secondmentioned layer.

2. A screen in accordance with claim 1, wherein the depth of the roughening is 20am. 2

3. A screen in accordance with claim 1, wherein the depths of the roughening consist of sack openings located close to each other and having bases, the secondmentioned layer covering said bases.

4. A screen in accordance with claim 1, wherein the first-mentioned layer consists of cesium iodide, the second-mentioned layer consists of gold and said photocathode is a layer containing antimony and cesium.

5. A screen in accordance with claim 1, wherein the second mentioned layer consists of titanium monoxide. 

1. AN INLET SCREEN FOR INTENSIFYING X-RAY IMAGES, COMPRISING A CARRIER, A LAYER CARRIED BY SAID CARRIER AND ADAPTED TO LUMINESCE UNDER THE ACTION OF X-RAYS, A PHOTOCATHODE CONNECTED WITH SAID LAYER, AND ANOTHER LAYER LOCATED BETWEEN SAID CARRIER AND THE FIRST-MANTIONED LAYER AND ABSORBING THE LIGHT OF THE FIRST-MENTIONED LAYER, SAID CARRIER BEING ROUGHENED PRIOR TO THE APPLICATION OF THE SECOND-MENTIONED LAYER, THE DEPTH OF
 2. A screen in accordance with claim 1, wherein the depth of the roughening is 20 Mu m.
 3. A screen in accordance with claim 1, wherein the depths of the roughening consist of sack openings located close to each other and having bases, the second-mentioned layer covering said bases.
 4. A screen in accordance with claim 1, wherein the first-mentioned layer consists of cesium iodide, the second-mentioned layer consists of gold and said photocathode is a layer containing antimony and cesium.
 5. A screen in accordance with claim 1, wherein the second-mentioned layer consists of titanium monoxide. 